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Part-IResults and Discussion3.1.1d The reaction of enamines (derived from ketones and morpholine or piperidinewith alkyl cyanoacetate) and elemental sulfur. 153.1.1a Condensation of α-Mercaptoketones or Aldehydes with Alkyl CyanoacetatesIn one of the versions 16-18 of the Gewald reaction, an α-mercaptoketone or aldehyde istreated with an active methylene nitrile bearing an electron withdrawing group, such as;methyl/ethyl cyanoacetates, malonitrile, benzoylacetonitrile or p-nitrobenzyl cyanide insolvents such as ethanol, dimethylformamide or dioxane in the presence of a catalystsuch as triethylamine, diethylamine or piperidine at around 50 o C (Scheme-1). The α-mercaptoketone or aldehyde is often generated in situ by the reaction of an alkali sulfidewith an appropriate α-halocarbonyl compound. The detailed mechanism of the reactionhas not been demonstrated, but it seems likely that the aldol-type condensation occursfirst, followed by an attack of the thiolate on the cyano group (Scheme-2). This particularversion of Gewald reaction has several drawbacks such as;i. it utilizes the starting compounds which are unstable and difficult to prepareii. this methodology is limited to aliphatic α-mercapto derivativesiii. non-activated nitriles such as cyanoacetic acid and benzyl cyanide do not undergothe Gewald reaction.R 2XR 1O+ Na 2 SR 2SHR 1O+YCNS2 o or 3 o amineR 2R 1SYNH 2X = Halo, R 1 , R 2 = H, alkyl, aryl, cycloalkyl, heteroarylY = CN, COOEt, COPh, CONHRScheme 1R 2OR 1 +HHYCNR 2YNR 1 SHSHBR 1YR 1YR 2SNH 2R 2SNHScheme-2. Mechanism for Scheme-167